1 files changed, 35 insertions, 0 deletions
diff --git a/whisper/topic.go b/whisper/topic.go
new file mode 100644
index 000000000..10069c902
--- /dev/null
+++ b/whisper/topic.go
@@ -0,0 +1,35 @@
+// Contains the Whisper protocol Topic element. For formal details please see
+// the specs at https://github.com/ethereum/wiki/wiki/Whisper-PoC-1-Protocol-Spec#topics.
+
+package whisper
+
+import "github.com/ethereum/go-ethereum/crypto"
+
+// Topic represents a cryptographically secure, probabilistic partial
+// classifications of a message, determined as the first (left) 4 bytes of the
+// SHA3 hash of some arbitrary data given by the original author of the message.
+type Topic [4]byte
+
+// NewTopic creates a topic from the 4 byte prefix of the SHA3 hash of the data.
+func NewTopic(data []byte) Topic {
+	prefix := [4]byte{}
+	copy(prefix[:], crypto.Sha3(data)[:4])
+	return Topic(prefix)
+}
+
+// String converts a topic byte array to a string representation.
+func (self *Topic) String() string {
+	return string(self[:])
+}
+
+// TopicSet represents a hash set to check if a topic exists or not.
+type TopicSet map[string]struct{}
+
+// NewTopicSet creates a topic hash set from a slice of topics.
+func NewTopicSet(topics []Topic) TopicSet {
+	set := make(map[string]struct{})
+	for _, topic := range topics {
+		set[topic.String()] = struct{}{}
+	}
+	return TopicSet(set)
+}